This invention relates to a process and apparatus for piecing a yarn at a spinning unit of an open-end friction spining machine of the type having a plurality of spinning units. Each spinning unit has two friction rollers that are drivable in the same rotational direction and are arranged next to one another to form a wedge-shaped yarn forming gap. Each spinning unit also includes a feeding and opening device with a feeding roller for the feeding of a sliver and with an opening roller for opening the fed sliver into individual fibers to be fed to the wedge-shaped gap. A suction device is provided for withdrawing the formed yarn in the direction of the wedge-shaped gap. Also provided are a device for winding the yarn onto a spool and a device for monitoring the yarn, which in the case of a yarn breakage, interrupts the feeding of the sliver by interrupting the drive of the feeding device. For the piecing process, a yarn end taken off the spool is returned to the wedge-shaped gap and pieced by means of a yarn piecing to the fibers that were fed by switching the feeding device on again.
An open-end friction spinning unit is known (EP-OS No. 34 427), where a piecing is to take place manually. In the case of this spinning unit, only one of the two rollers is formed as a so-called suction roller having a perforated shell and an interior suction insert aimed at the area of the wedge-shaped gap by means of a suction slot. The other roller has a closed shell surface that is equipped with fittings. In the case of a yarn breakage, the continued feeding of the sliver is interrupted via the yarn guard, while all other drives continue to run at the same speed, i.e. the opening roller, the friction rollers, the withdrawal rollers and the wind-up device. For the piecing process, the spool is lifted off its drive. Then the yarn end is withdrawn from the spool and is cut to length in such a way that the resulting end reaches into the area of the fiber feeding point of the wedge-shaped gap. Subsequently, the yarn end is returned to the area of the wedge-shaped gap, the effect of the suction device being interrupted in a controlled manner so that the yarn end is located in the spinnng unit at a distance from the wedge-shaped gap. Then the suction device is switched on again so that the yarn end arrives in the wedge-shaped gap of the turning friction rollers. Subsequently, the feeding of the sliver is to be switched on again by the switching-on of the drive of the feeding roller and the withdrawal and the winding-up of the yarn is to be switched on again by the lowering of the spool to its withdrawal device. The quality of the piecings with this arrangement depends on the skill of the operating person. But it was found that it is impossible to produce a piecing of the same quality and the same appearance during each piecing process. This unreliability and inconsistency with respect to the quality of the piecing have the result that the spool of yarn produced by means of this device cannot be used immediately during a further processing operation. It is necessary to let the spool of yarn run through a spooling machine and in the process clean out the piecings (if necessary, also other faults in the yarn) and to replace them by another yarn connection, such as a knot. However, such an additional process considerably reduces the cost-effectiveness of friction spinning.
The invention is based on the objective of improving the start spinning at a spinning unit after a yarn breakage in such a way that high-quality piecings are obtained which, with respect to quality, differ so little from the normally spun yarn that they need not be cleaned out so that the produced yarn can be directly processed further with these piecings.
This objective is achieved by providing according to the invention that the quantity of the fibers to be pieced with the returned yarn end is adjusted to a constant value for each start spinning process by feeding to the opening roller for each start spinning process a sliver end that has the same quality.
The invention is based on the consideration that, irrespective of the type of the actual piecing process, it is a basic requirement that the quantity of fibers made available for the piecing process must in each case be exactly the same because otherwise piecings of differing quality will be obtained.
In preferred embodiments of the invention, it is provided that before the actual piecing process, the sliver feeding device is switched on for a predetermined period of time, and within an exactly defined time interval before the start of the actual piecing process, is switched off again, the fibers that were opened up into individual fibers by the opening roller during this process being led out of the spinning unit. This process takes the fact into account that constructively, it is simpler not to interrupt the opening roller in the case of a yarn breakage but to let it continue to run. Only the feeding of the sliver is interrupted which, however, has the result that the end of the sliver, the so-called tuft or fiber beard, is continued to be combed out and thinned out by the opening roller meshing into it, so that as a function of the time interval between a yarn breakage and the connected switching-off of the sliver feeding device and the switching-on again of the sliver feeding device for a piecing process, very different sliver ends or fiber beards may occur containing a differing quantity of fibers. By means of the brief switching-on and switching-off of the fiber feeding in a defined interval before the actual piecing process, it is ensured that for the piecing process, a sliver end is present that has the same characteristics irrespective of the period of time for which the concerned spinning unit was stopped after a yarn breakage until the start of the piecing process.
In a further development of certain preferred embodiments of the invention, it is provided that the fibers opened during the feeding of the sliver that precedes the actual piecing process are fed to the wedge-shaped gap, and, by means of a subsequent cleaning of the wedge-shaped gap, are removed before the start of the actual piecing process. Since a cleaning of the wedge-shaped gap before the actual piecing process is practically always part of the complete piecing program, the additional expenditures are very low.
In a further development of preferred embodiments of the invention, each spinning unit is equipped with an auxiliary suction means leading out into the area of the wedge-shaped gap and acting on the exterior shell surfaces of the friction rollers, said auxiliary suction means being connected to a vacuum source at least during the feeding of the sliver preceding the actual piecing process. By means of this auxiliary suction means, a cleaning process can be carried out in a simple way during which the fibers are removed which were fed to the wedge-shaped gap during the switching-on of the feeding device for the purpose of the preparation of the fiber beard or tuft. If necessary, it is also contemplated by means of this cleaning to remove the dirt and fiber residues which remain in the area of the wedge-shaped gap after the yarn breakage and which are twisted into a cocoon/caterpillar shape. In order to facilitate the cleaning by means of the auxiliary suction means, it is advantageous to interrupt the drive of the rollers at least during the feeding of the sliver preceding the actual piecing process. For the same purpose, it is advantageous to switch off or throttle the effect of the suction device at least during the feeding of the sliver preceding the actual piecing process. This cancels or at least reduces the forces holding the fibers and the yarn in the wedge-shaped gap during the spinning so that the fibers and the dirt can be removed relatively easily. In order to detach the fibers or fiber residues and dirt from the area of the wedge-shaped gap, it is provided in another development of the invention that the suction device, while the auxiliary suction means is switched on, is connected at least for a short time to a high pressure source. This generates an air current coming from the inside of the rollers and going in the direction of the auxiliary suction means by means of which a very effective cleaning can be carried out.
In a further development of preferred embodiments of the invention, it is provided that the spinning units are equipped with a removable covering for the wedge-shaped gap, that a cleaning device is provided that can be applied to the exposed wedge-shaped gap, and that the cleaning device is applied to the wedge-shaped gap after or during the feeding of the sliver preceding the actual piecing process. By means of this additional cleaning device which may also contain mechanical cleaning means, a very effective cleaning is made possible, removing at the same time also from the area of the wedge-shaped gap the fibers opened during the switching-on of the feeding device of the sliver preceding the piecing process and transported into the area of the wedge-shaped gap.
In a further development of preferred embodiments of the invention, it is provided that a fiber feeding channel connecting the opening roller of each spinning unit with the wedge-shaped gap can be exposed at least partially, and that during the feeding of the sliver preceding the actual piecing process, a device for receiving the individual fibers is applied to the at last partially exposed fiber feeding channel of each spinning unit. In the case of this arrangement, the fibers that were made into individual fibers during the preparation of the sliver, do not even reach the area of the wedge-shaped gap but are intercepted beforehand and led away. Another cleaning of the wedge-shaped gap is therefore not necessary.
In a further development of preferred embodiments of the invention, it is provided that the auxiliary suction means of each spinning unit opens out into a fiber feeding channel connecting the opening roller with the wedge-shaped gap, and that the fiber feeding channel is closed behind the mouth of the auxiliary suction means during the feeding of the sliver preceding the actual piecing process. In this manner, a type of short or shortcut is produced between the auxiliary suction means and the opening roller, by means of which the fibers made into individual fibers during the preparation of the fiber beard are led off directly without arriving in the wedge-shaped gap. In this case, the spinning unit itself does not have to be opened because only a direct connection is produced between the auxiliary suction means and the fiber feeding channel.
In a further development of the invention, it is provided that before the actual piecing process, the feeding of the sliver is switched on for a certain time period and is subsequently switched off again, the end of the sliver that is present after the switching off being moved back from the area of the opening roller and the fibers that were made into individual fibers by the opening roller before the actual piecing process being led out of the spinning unit. By means of the moving-back of the sliver after the preparation of the fiber beard, this fiber beard is disengaged from the opening rollers so that, on the one hand, it receives a certain shape and is, on the other hand, no longer combed out. This measure is advantageous when a relatively long period of time, for example ten seconds or more, passes between the preparation of the end of the sliver, the so-called fiber beard, and the actual piecing process. It is then prevented that during this time period fibers are still combed out and transported into the area of the wedge-shaped gap which could interfere with the piecing process.
In a further development of preferred embodiments of the invention, it is provided that the yarn withdrawal device and/or the feeding device of the fibers and/or the drive of the rollers, during the production of the piecing, are temporarily operated at speeds that are reduced in comparison to the operational speed, the speeds being coordinated to one another in such a way that a yarn count is spun which corresponds to the yarn count spun at operational speeds. In this case, a special advantage of friction spinning is utilized, where it is possible to spin the same yarn count even when the speeds vary. Because of the reduction of the speeds, longer time periods are made available for the individual process steps of the actual piecing process so that these can be proportioned and adapted to one another more precisely. In this case, it is advantageous that the speeds are increased to the operational speeds in such a way that also during the increase, the same yarn count is spun. Thus a uniform yarn is obtained so that the quality of the spool is not impaired.
In a further development of preferred emoodiments of the invention, in the case of an open-end friction spinning machine having a plurality of spinning units, a servicing apparatus is provided that can be moved along the machine and can in each case be applied to a spinning unit, said servicing apparatus being equipped with means for carrying out a piecing process at a spinning unit. In especially preferred embodiments the servicing apparatus contains means for actuating the feeding device that can be switched on before the actual piecing process for an indicated period of time and are switched off again for an exactly defined time period until the actual piecing process. This results, on the one hand, in a reduction of the manufacturing expenditures for an automatic piecing since the means for carrying out the individual process steps in most cases exist only once, namely in the servicing apparatus and not at each spinning-unit. On the other hand, the advantage is achieved that the individual process steps are carried out by always the same means so that it is ensured that the same conditions exist and can always be reproduced. This applies in particular also to the means by which the fiber beard is prepared in such a way that it has the same characteristics before each piecing process.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.